If $x \veebar y = 3x+y$ and $x \bigtriangleup y = x^{2}-2y^{2}$, find $-2 \veebar (2 \bigtriangleup -1)$.
Solution: First, find $2 \bigtriangleup -1$ $ 2 \bigtriangleup -1 = 2^{2}-2(-1)^{2}$ $ \hphantom{2 \bigtriangleup -1} = 2$ Now, find $-2 \veebar 2$ $ -2 \veebar 2 = (3)(-2)+2$ $ \hphantom{-2 \veebar 2} = -4$.